Rocky Alien Worlds May  Support Life

Need To Be Young 

As search for life in the universe

 continues, scientists already know it's not enough to find rocky planets in a star's habitable zone, the region where a planet can host liquid water

Liquid water is just the 

starting point Indeed, other factors, such as nitrogen, may play a role in a planet's habitability, as well as the ratio of land to sea.

A team of scientists suggests

 that one of the key characteristics of a life-supporting, rocky exoplanet is that it must be young — just a few billion years old at most. 

To support life, a planet needs 

enough heat to power a carbon cycle, which is typically created due to the radioactive decay of elements such as uranium and thorium. 

Lead author Cayman Unterborn, a

research scientist at the Southwest Research Institute said "Exoplanets without active degassing are more likely to be cold, snowball planets,"    

That radioactive decay, in turn,

 causes volcanic degassing — the release of gasses held within a planet into the atmosphere through volcanoes — on the surface of a planet.

Degassing contributes CO2 to

  the atmosphere and continues the carbon cycle. But older planets might have consumed their radioactive resources and thus may not be able to retain their heat